The present invention generally relates to amplifiers, and more particularly to methods and apparatus for amplifying a telecommunication signal.
Distributed amplifiers and mixers have been used extensively for many years in a variety of broadband system applications such as microwave receivers, wide-band transmitter exciters and low noise oscilloscope preamplifiers. Distributed amplifiers are conventionally configured to employ multiple amplifier cells within the distributed transmission line networks. The conventional configuration of multiple amplifier cells within distributed transmission line networks generally exhibits the desired increase in gain. However, the efficiency of the conventional configuration of multiple amplifier cells within the distributed transmission line networks degrades with a reduction in drive power.
Referring to FIG. 1, a distributed amplifier 10 is illustrated according to the prior art. The distributed amplifier 10 is shown with multiple cells (12, 14, 16). Each of the cells (12, 14, 16) includes a field effect transistor (FET) 18. The drain terminal 20 of the FET 18 of each of the cells (12, 14, 16) are coupled with output-line inductances 22, which are connected to an output-line ground 24 with an output-line termination resistance 26. The gate terminals 28 of the first FET 18 of each of the cells (12, 14, 16) are coupled with input-line inductances 30 that are connected to an input-line ground 32 with an input-line termination resistance 34.
The distributed amplifier 10 of the prior art as illustrated in FIG. 1 has a lower output with a reduction in the drive power. However, the Direct Current (DC) power consumption is not substantially reduced so that the Power-Added Efficiency (PAE) of the distributed amplifier 10 of the prior art degrades as a function of the output power (Pout) An example of PAE degradation as a function of the output power (Pout) for a distributed amplifier of the prior art is illustrated in the graph of FIG. 2.
This PAE degradation as a function of output power (Pout) is especially evident when the distributed amplifier 10 of the prior art is utilized to amplify a telecommunication signal, such as a Code Division Multiple Access (CDMA) signal, a Time Division Multiple Access (TDMA) signal and a Global System for Multiple access (GSM) signal. This PAE degradation as a function of output power (Pout) in amplifying a telecommunication signal is at least partially due to the sizing of the distributed amplifier for peak power. Since the distributed amplifier is sized for peak power but operates predominantly at the average power level of the telecommunication signal, a typical distributed amplifier configured for amplification of the telecommunication signal exhibits less than desirable PAE.
In view of the foregoing, it should be appreciated that it would be desirable to provide methods and apparatus for amplifying a telecommunication signal with the apparatus and methods providing a PAE that is not substantially affected by a reduction in the drive power. Furthermore, additional desirable features will become apparent to one skilled in the art from the drawings, foregoing background of the invention and following detailed description of a preferred exemplary embodiment, and appended claims.